Refrigeration & Air Conditioning

WEIGHTAGES

CA MTE ETE

Attd AT P P Th P Th

05 20 0 0 25 0 50

L T PCREDITS

(or Max. Marks)

3 1 0 4

TEXT BOOK: Refrigeration and Air-Conditioning (For Polytechnics), Katson books by R. K. Rajput (S.K. KATARIA & SONS publications). Revised edition: 2008-09, Reprint: 2010.

REFERENCE BOOK: A Text Book of Refrigeration and Air-Conditioning by Sandeep Bajaj, Ishan Publications, First edition: 2006.

Lecture 1

Mechanism of producing cold.

Principles of cooling effect.

Laws of refrigeration.

Refrigeration & its ways.

Mechanism of producing cold.

Cold is a relative term used to denote low temperature. It is a final result which is obtained by certain condition i.e caused by extraction of heat.

A refrigerating system produces a condition called cold by the process of extracting heat from refrigerated space. ( comparable example:- water soaked out from the vessel with the help of sponge)

In refrigerator a substance called refrigerant is used in such a way that it soaks up heat from refrigerated space and is then passed to the outside box where heat is squeezed out.

Principles of cooling effect.

By chemical means

By contact cooling

By supplying energy

By chemical means

In this case a chemical reaction is used for producing the cold. These chemical reaction requires heat for its competition and that heat is taken from the refrigerated space (to be produced). E.g salts like NaCl, CaCl2, when dissolved into water, absorbs heat and cool the water much below than 00 C.

CaCl2- Lowers the water temp upto -500 NaCl- Lowers the water temp upto -200

By contact cooling

In this method the substance to be cooled is brought in the contact (directly or indirectly) with a cooling medium, such as ice or cold water.

By Supplying energyIn this case energy is supplied in the form of

heat or work, to operate a heat pump by which heat may be abstracted from the substance and rejected in the atmosphere.

Laws of refrigeration

1.

2. The temp at which a change of state occurs remains constant throughout the change if the pressure remains constant. This is applicable for both evaporator and condenser.

3. Heat will flow from a body at a higher temp to a body at a lower temp. This is also applicable for both evaporator and condenser.

4. While selecting metals, only those metals are selected which have a high thermal conductivity. Cu, Al.

5. Heat energy and other forms of energy are mutually convertible.

Refrigeration and its ways

In simple refrigeration means the cooling or removal of heat from a system. Refrigeration is generally produced via three ways.1. By melting of solid2. By sublimation of solid3. By evaporating a liquid